Cambridge
School of Navigation John Starkie, PhD, RNR
P Papa
The Blue Peter
All aboard, vessel is about to proceed to sea.
(At sea) your lights are out or burning badly
Packet, Paddle, Pail, Paint, Painter, Pannikin, PanPan, Parallel, Parallel rule, Parbuckle, Parcel, Parley, Parrel, Part, Partner, Passage, Passenger, Passport, Patch, Paunch, Pawl, Pay, Pay off, Peak, Pelagic, Pendant, Pennant, Petrol, PFD, Piece, Pier, Pig, Pillar, Pilot, Pilotage, Pilot boat, Pilot book, Pilot Jack, Pin, Pinnace, Pinrail, Pintle, Pipe, Pipe down, Piping the side, Pirate, Piracy, Pitch, Pitchpole, Plain sailing, Plane, Plane sailing, Plank, Plate, Plimsoll line, PLB, Plotter, Plug, Plumb, Portland plotter, Douglas protractor, Point, Points of sail, Polacre, Pole, Pollution, Pontoon, pontoon boat, Poor, Poop deck, Port, Portsmouth yardstick, Port tack, Position, Position line, Praam, Pram, Precipitation, Preferred channel marker, Press gang, Pressure, Preventer, Prime meridian, Privateer, Prize, Proa, Projection, Promontory, Propeller, Prop walk, Protractor, Provision, Prow, Pudding, Pulley, Pulling boat, Pulpit, Pump, Punt, Purchase, Purser, Pulpit, PY, Pyrotechnic
Packet
n A vessel employed to carry the mail.
A vessel following a regular schedule.
n A container of small items or documents, usually made of paper or cardboard, often in a waterproof container, and sealed with gum, glue or wax.
Paddle
n A short, oar-like tool used over one side of a canoe, without a crutch, for moving the canoe through the water.
n A long thin oar-like tool with a blade at each end; the blades are dipped alternately on different sides of the kayak to propel the boat through the water.
n One of many large, flat boards attached to a wheel at each side of a vessel (a paddle steamer) to drive the vessel through the water. Mississippi river boats were characterised by having a single paddle wheel at the stern.
n The flat board which closes the aperture in a lock gate: the aperture allows water to flow from a higher part of the lock to a lower part. The paddle is raised and lowered by a toothed bar riding on a toothed wheel operated by a windlass.
In the East of England paddles are called slackers.
v To use a paddle to propel a canoe or kayak through the water.
Paint
n A pigmented viscous, or semi-viscous liquid used to cover wood or metal with a thin layer which dries or 'cures' to a hard layer. paint is intended to enhance the appearance of the substrate and to prevent (or retard) its degradation by water, air or environmental factors.
v To apply a thin layer of paint to a surface, using a brush, roller or foam pad.
Painter
n A line attached to the stem of a dinghy.
A shank-painter is a line or a chain from one of the bows or topside of a ship to support the flukes and crown of the anchor when the shank is at the cathead.
Chatterton states that "Mr Oppenheim derives this . . . word from the old French "pantiere, . . . a noose."
n A person who paints.
Pannikin
A cup with a long handle, rather like a ladle, for drinking.
PanPan
A VHF radio call to alert the authorities (the MCA) that the vessel is in trouble but has no emergency and can cope.
Parallel
Parallel of latitude, or parallel lines of latitude. Parallel lines never diverge or converge however far they are extended in either direction, unlike the meridians of longitude which converge at the poles and diverge at the equator.
Parallel rule
A pair of rules linked together by two (or more) articulated links so that the two rules always remain parallel to one another. They are used to transfer a position line from one part of a chart to another.
In small vessels a parallel rule is likely to be replaced by a Portland plotter or even a Douglas protractor.
Parbuckle
A method of lifting a cylindrical object, such as a spar or a barrel, using a pair of lines passed around the object and using the object as a moving sheave.
Leeboards are often raised with a line attached to the side of the boat, passed through a sheave in the leeboard and back up to the boat.
Drawing from Knox-Johnston
Parcel
To enclose a line (such as a stay or shroud) in strips of tarred canvas to protect it from the weather.
Present-day (early 21st century) sailors are more like to use waterproof plastic self-amalgamating tape.
Parley
Truce talks. A discussion between enemies.
Parrel
A loop or collar of line, often laced with wooden (now plastic) beads. A parrel may be used to keep a gunter 'yard' or lugsail yard or a square yard close to the mast.
Partner
A framework designed to strengthen the deck at a point where a mast or other device or structure passes through.
Passage
A voyage. A vessel is 'on passage' when sailing from one place to another. There is an implication of being out of sight of land.
The Passage Plan (Annexe 23) which all vessels are required to prepare includes pilotage
Passenger
Someone carried on a vessel for reward: someone who pays to be carried on a vessel. Passengers might pay for simply being carried from one port to another, or for accommodation, or for food, or for entertainment, or any or all of these.
Members of the crew are not passengers.
The master of the vessel is qualified according to the number of passengers which can be carried: the vessel is licenced for the number of passengers carried.
Passport
A document, specific to a single person, required for that person to travel beyond a national boundary or to return to their country.
Patch
Damaged planking may be repaired with replacement of the plank(s) or by cutting out the damaged wood and fitting in a small piece: a Dutchman.
Paunch
n A thick strong mat of woven line used to prevent parts of a ship from chafing against other parts.
Similar to a rope fender., except that a fender is used on the outside of the ship to prevent it chafing against another vessel or a quayside.
n A beer belly.
Pawl
The lever or ratchet arm which engages on a toothed wheel to prevent a capstan (winch) or windlass from turning backwards.
Pay
To pay a seam between planks is to pour hot pitch and tar into it after it has been caulked.
To pay out a line or rode is to increase the scope hand over hand, gradually, rather than releasing all the line at once.
To pay the piper is to give money to the piper in exchange for his playing the tune called.
To pay in kind is to give something other than money (the village children?) in exchange for the service rendered.
Pay off
To allow the head of a vessel to turn to leeward.
Peak
n The top after corner of a four-sided fore-and-aft sail. The top corner of a triangular sail.
The upper tip of a gaff or yard.
vb To peak a gaff or yard (with its sail) is to raise the peak higher with the peak ha'lyard.
See Forepeak.
Pelagic
Pertaining to the open sea. Pelagic fish are those fish which live in the open sea rather than inshore, or in estuaries or rivers.
Pendant
A line secured at one end to a spar and at the other to a block.
Pennant
A long thin flag flown from the masthead of a naval vessel. Commodores and admirals would fly their own distinguishing pennants.
In 1610 it was 'a rope for hoisting' and was probably a confusion by semi-literate sailors between 'pendant' (suspended rope) and 'pennon' (a long narrow flag).
By 1690 it meant 'a flag on a warship' and by 1815 Falconer used it to mean 'a sort of long narrow banner'.
In 1880 it was used to mean 'flag symbolizing a sports championship'.
Falconer, in 1815, used the word 'pendant' to mean a long, narrow, often swallow-tailed banner flown from the mast-head (now the top of the mast) and also to mean a length of line with a thimble or block on the end.
The modern distinction, given above, between 'pennant' and 'pendant' is somewhat artificial.
Petrol
A volatile mixture of hydrocarbons used as a fuel in some internal combustion engines and in some camping stoves.
Petrol is widely used in the engines of cars and outboard motors, but is now considered too dangerously volatile for inboard marine engines.
A contraction of 'petroleum' or 'petroleum spirit'.
Known as gasoline in the USA.
PFD
Personal Flotation Device, or buoyancy aid. Designed to help a person float in the water but not to keep an unconscious person afloat.
Not a lifejacket.
Pier
A raised structure, supported on posts or piles, extending some way out into the water.
Used for loading and unloading specialised cargo (such as oil) or for recreational purposes.
Pig
Of ballast, refers to masses of cast iron or lead. Usually offcuts rather than ingots.
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Pile, piling
Pillar
Vertical pieces of wood fitted under deck beams to support them.
When the mast of a yacht is stepped on deck it is often supported by a beam directly under the step. In turn, the beam is often supported by a pillar stepped on the keel.
Pilot
A navigator with great experience of and expertise in a specific port or approach. Ship's captains employ pilots to help them navigate their ships into and out of harbours.
Pilots are taken to, and brought from ships on pilot boats or helicopters. They board and leave the ships at designated Pilot Boarding Points marked on the charts.
Pilotage
Navigating the boat with reference to visible 'signposts' such as buoys, lights, withies and (most usefully) transits. Pilotage is to be distinguished from offshore navigation (passage-making) where there are no visual aids, and navigation is by dead reckoning (or GNSS).
Ships are required to use a pilot, a person who has detailed knowledge of the area, to assist the Captain with pilotage into and out of harbours.
Small boat pilotage begins at the berth and ends at the SWM, where the passage begins; or it begins at the SWM (where the passage ends) and ends at the berth.
The plan should be prepared beforehand and should be in the cockpit: there should be no need to visit the chart table.
Headings are not used in pilotage.
To approach a buoy which bears, say, 055°M the boat should not be pointed toward the buoy on a heading of 055°M because the tide will move it off course. (A GIF in preparation)
Instead, point the boat on a heading uptide of the bearing at an angle which keeps the buoy on the bearing; the boat’s heading must be found by trial and error. Following a bearing needs two people: one to helm the boat; the other to use the hand-held compass.
To leave a buoy on a course (not a heading) of, say, 025°M the buoy should be kept on a backbearing of (025° + 180° = 205°M).
Similarly, clearing bearings need two people: one to helm and another to use the hand-held compass.
When following a transit, the heading is not the bearing of the transit but must be found by trial and error. The helmsman can follow a transit without assistance (remember that the helmsman is not a lookout).
A back-transit may be followed in a similar way, with the helmsman looking aft.
All the visual aids should be marked on the pilotage plan, and named, so that they can be ticked off as they are passed.
Dangers and features to be seen, but perhaps not used, should be marked.
Distances between changes of direction (so-called ‘wheel-over’ points) should be noted, along with the time to be taken for each traverse.
1 Pilotage Narrative Plan
Use the words ‘follow’ or ‘keep’ . . . . ‘until’
For example,
Follow transit Fl.G.2s & Fl.G.3s on 172°M until 2FG(vert) bears 203°M (3 minutes).
Keep 2FG(vert) on bearing 203°M until ECM bears 195°M (1.5 minutes).
The narrative plan has the advantage of being explicit.
For example:
From Snakecatcher's Bay,
KEEP house on a backbearing of 224° UNTIL Oc G 10s & Oc R 10s & Fl G 20s in transit on 110°T (about 12 minutes at 5 kn)
KEEP Oc G 10s & Oc R 10s & Fl G 20s in transit on 110° UNTIL Fl G 2s & Oc G 4s in transit on 154°T (about 11 min)
KEEP Fl G 2s & Oc G 4s in transit on 154°T between the breakwater walls UNTIL marina entrance bears 130°T (about 18 min)
KEEP marina entrance on bearing 130°T UNTIL inside the marina. (about 10 min)
2 Pilotage Linear Plan
The course to be followed, however winding, is drawn as a straight line starting at the bottom of the page.
Each change of direction is shown as an arrow to the right or the left of the line with the new bearing (not heading!) marked.
The buoys to be passed are drawn (as symbols) on the correct side of the course to be followed. They should be named on the plan, and ticked off as the plan is followed.
The linear plan has the advantage of being a ‘head-up’ plan; the boat and the helmsman are always following the straight line.
For example:
3 Pilotage Sketch Plan
Artistic sailors can draw a sketch plan of the approach (or departure) with buoys (named) in their relative places and the course to be followed drawn on the plan.
A tracing and annotation of the chartlet in the pilot book might be useful.
Pilot book
A book giving detailed descriptions of the hazards, buoyage and approaches to harbours in a specified area.
The chartlets may be more detailed, and to a bigger scale, than a chart; there are photographs and text to amplify the chart detail. There is often historical, cultural and social detail about the harbour and country.
Pilot Jack
A (British) Union Flag surrounded by a white border flown on a jackstaff at the stem of a merchant vessel. It indicates that the vessel either needs a pilot or has a pilot on board.
Pin
n Of a block (a pulley) the pin is the axle of the sheave.
n A belaying pin is a metal or wooden pin, fitted into a hole in the fife rail and pinrail, to which halyards and sheets are belayed.
Pinnace
A small boat, with fewer than eight oars, for carrying officers other than the Captain.
In Falconer's day (around 1815, it was also " a small vessel, navigated with oars and sails, and having . . two masts, rigged like . . a schooner."
See barge.
Pinrail
A railing on each side of the ship abeam of the masts, fitted with belaying pins for securing ropes.
See Fife rail
Pipe
n The instrument (boatswain's pipe, or whistle) which the boatswain uses to give standard instructions.
Unrelated to, but somewhat similar in appearance to, a smoker's pipe.
n The signal, or instruction, given by the boatswain's pipe.
v To give instructions by sounding the boatswain's pipe or whistle.
Pipe down
The pipe, or signal, for 'lights out' at the end of the day.
coll Noisy children may be told to "pipe down"; to be quiet.
Piping the side
A ceremonial signal on the boatswain's pipe when a senior officer boards or leaves the ship.
In the Age of Sail the officer would use the ladder on the side of the ship, holding the manropes which, in turn were held away from the side of the ship by side-boys. The pipe would begin as the officer's hat appeared above the gangway; as he left the ship the signal would end as his hat disappeared below the gangway.
Pirate
A criminal who boards vessels without permission to rob and kill the crew and passengers and to steal the vessel.
See Privateer.
Piracy
The act of being a pirate; of boarding, robbing and killing.
Pitch
v A boat pitches when the stem and stern alternately rise and fall. Oscillations, or changes of attitude, in the horizontal transverse plane about the beam axis.
n A black, tarry substance used to waterproof the seams between the planks of a carvel boat.
n The pitch of a propeller blade is the angle it has to the propeller shaft. If the pitch is fixed the speed of the vessel is controlled by the speed of the engine. If the pitch is variable the engine can be held at a steady, optimum, speed and changes to the pitch of the propeller change the speed, or direction, of the vessel.
Pitchpole
When a boat capsizes stern over stem, rather than by rolling sideways.
Plain sailing
A modern-day misunderstanding of 'plane sailing'.
As used in the late 20th and early 21st centuries 'plain sailing' might refer to sailing under simple sails, such as mainsail and genoa for a sloop, jib, mainsail and mizzen sail for a ketch.
Plane
v To skim, or skip, over the surface of the water, rather than pushing through it.
See Displacement.
n A flat-soled tool, with a sharp blade (iron), for removing thin shavings of wood.
n A contraction of aeroplane.
adj Flat. A table top is a plane, or planar surface.
Plane sailing
A plane (or planar) chart is one which is flat, with meridians all parallel as well as the parallels of latitude; usually Mercator's projection.
Plane sailing is navigation with a plane chart.
An alternative to plane sailing, with a globe, is rarely practiced today.
Another alternative, using polar projections to plot great circles, is commonly used for navigating long distances.
Astronavigation cannot be regarded as 'plane sailing': the calculations use 3-dimensional and circular angles, as do GNSS instruments.
Plank
A length of wood which is significantly longer than it is wide, and significantly wider than it is thick. The term usually refers to the planks along the sides of a wooden vessel.
Where the vessel is longer than a single plank, they are joined (scarphed) end-to-end to form strakes the full length of the vessel: a strake is a run of planking along the side of a wooden vessel.
A strake which is thicker than its neighbours, for extra strength or attachment, is a wale. (Not a whale, which is a marine mammal). Thus a gunwale is a thicker strake pierced for gun ports; a chainwale (cha'n'l) is a thicker strake for the attachment of the shroud chains.
Plate
n A piece of metal welded or riveted to other plates to construct a steel ship.
n A chainplate is a strip of metal attached to the topside of a yacht or dinghy to which the lower ends of the shrouds are attached and which distribute the tension of the shrouds through the hull They are usually present where there are no ribs or frames to distribute the tension.
PLB
Personal Locator Beacon
A small electronic device which can be attached to a lifejacket. When activated the PLB broadcasts radio signals, which are relayed by satellites to the rescue services, giving the location of the device.
Plimsoll line
Markings on the side of a ship which show the water levels to which the ship may be loaded in waters of different temperature and salinity.
TF: Tropical Fresh Water
F: Fresh Water
T; Tropical Seawater
S; Summer Temperate Seawater
W; Winter Temperate Seawater
WNA; Winter North Atlantic
Prefix L; Lumber (Timber)
L⦵R; Lloyd's Register
Plotter
A rule with scales (often circular and sliding) for drawing rhumb lines and for measuring angles on a chart. On a small chart table the Portland Plotter is more useful than parallel rules: the Douglas Protractor is useful on a very small chart table.
Portland Plotter
To draw a rhumb line at a chosen angle, set the angle in the circular sliding scale. Put the pencil point on the chart, and slide the edge of the plotter to the pencil point. Rotate the entire plotter so that the small arrows point to True North (align the graticule of the circular scale with a meridian or a parallel). The large arrow shows the direction of the rhumb line.
To measure the angle of a given rhumb line, align the edge of the plotter, or one of the long scribed lines, with the rhumb line; ensure that the large arrow points in the correct direction. Turn the circular scale so that the small arrows point to True North. Read the direction (angle) from the scale.
Douglas Protractor
To draw a rhumb line at a chosen angle, place the pencil point on the chart and slide the edge of the plotter to the pencil point. Align the central point or hole of the plotter, and the angle on the inner scale, on a meridian. Draw the rhumb line along the side of the plotter.
To measure the angle of a given rhumb line, align the edge of the plotter with the rhumb line, ensuring that the arrows point in the correct direction. Slide the plotter along the line until the central hole covers a meridian. The angle of the line can be read where the same meridian crosses the inner scale.
Plug
n A shaped item used to block a hole.
Yachts normally carry a set of wooden plugs (or bungs) each sized and shaped to fit a skin fitting. They are used to plug the hole if the fitting or its hole is damaged.
Some hawse-holes on yachts have plugs, but most now have a metal flap which also acts a chain snubber.
Dinghies often have a hole in the transom or bottom to drain out water when they are hauled ashore. There is a plug, or bung, often with a screw thread, to fit this hole and to keep the water out when the boat is sailing.
v To plug a hole is to insert a bung and so stop the flow of water.
Plumb
Referring to metallic lead. 'Plumbum' is the Latin word for lead (the metal).
A plumb line has a heavy lead weight at its end, and is used to make vertical lines and edges.
A mast is plumb if it is vertical.
Plumbing the depths uses a heavy lead weight on a 20 fathom leadline to measure the depth of water.
Plumbing is a craft which uses lead piping to carry water into and around dwellings and to carry waste away. Lead was replaced by copper during the 20th Century and then by plastic. People who install and repair water pipes are still called 'plumbers', although none of them now (early 21st Century) use lead.
Point
n One thirty-second of a circle; 11.25 degrees of arc.
The points of a compass, or the horizon, are the directions between each 11.25 degrees of arc; there are thirty two points of the compass, or horizon.
Points are very rarely used in navigation: they have been superseded by degrees of arc. On some vessels they are used by the lookouts to indicate the relative bearing of a feature. "The ship is two points abaft the starboard beam." "The lighthouse is one point on the port bow."
n The sharp tip of an object such as the leg of a drawing compass.
n A low arm of the shore which projects out into the sea, or river.
v Heading. A sailing vessel points to one side or the other of the wind. A vessel on a broad reach may point up closer to the wind onto a fine reach, or close-hauled.
v A person points to a ship on the horizon by extending a finger, and possible a whole arm, in the direction of the distant ship.
A person might point a gun by aiming it toward a target. If the target is very close it might be at point-blank range.
v To point a rope is to unlay the strands at the end, and then weave them around the remaining strands so that the end of the rope is firmly bound with its own strands and tapers to a point. See Graft.
The four Cardinal points are North, South, East and West.
Reef points are nettles passed through eyelets in the sail and are used to tie the bunt of a reefed sail into a neat bundle.
Points of sail
A sailing boat cannot sail directly toward the wind. Most boats cannot sail closer to the wind than 45° on either tack.
With the wind forward of the beam a boat may be close hauled, on a close or fine reach, or beating to windward. "Gentlemen don't sail to windward" because it's hard work, uncomfortable and wet. The helmsman must be alert to the wind in the sails; to keep as close to the wind as possible without pinching. The vessel is constantly plunging its bows into the swell and pitching over them. The constant pitching, and the wind from ahead, drives spray, and often water, across the boat and crew.
With the wind on the beam a boat is said to be on a beam reach, or to be reaching. For most boats a beam reach is the fastest and most comfortable point of sail. The vessel is sailing along the swell rather than pitching into it; the roll that might be engendered by the swell is dampened by the wind on the beam.
With the wind coming astern a boat is said to be running before the wind. For a square-rigged vessel this is its best point of sail. For a fore-and-aft rigged vessel this is a potentially dangerous point of sail. It is not possible to ease a Bermudan or gaff mainsail square to the centreline so the sail is almost always 'by the lee'; there is always a danger that a flaw of wind will back the sail and cause an unintended gybe. If the foresails are carried on the same side as the mainsail they are blanketed by the mainsail; if they are 'goose-winged' they need a skilled helmsman or a boomed foresail or both. With a following wind and a big swell there is a danger of broaching; the water near the top of the swell may be moving forward faster than the boat so that the rudder stalls; the boat may then turn across the wind and swell, and capsize.
With the boat hard on the wind the sails are sheeted in and the helmsman steers the boat for best speed to windward.
With the wind free the helmsman steers to a compass course and the crew trims the sails for best speed.
Polacre
A three-masted ship of the Mediterranean Sea. The three masts were pole masts with neither tops nor cross-trees. They had square-sails on the mainmast and lateens on the fore- and mizzen-masts. Neither the square nor the lateen yards had footropes.
Pole
n A long, thin wooden or metal cylinder, sometimes hollow.
adj A 'pole mast' is a mast made of a single piece of wood. Pole masts are now (early 21st century) the norm, so that the adjective 'pole' is almost always omitted. Modern wooden masts are often made of several pieces scarphed and glued together so that they look like a single piece. The glues and fittings used to scarph modern masts were developed long after the adjective 'pole' was abandoned.
The adjective has never been used to describe metal masts, which have almost always been of one piece.
n A punt pole is used by the punt operator standing at the stern of the vessel and pushing the vessel along with the end of the pole pushed against the river bed.
n The geographical poles of the Earth are the points on the surface of the Earth at the tips of the rotational axis of the Earth.
The magnetic poles are points where the lines of magnetic flux of the Earth are perpendicular to the surface.
n The Pole-star (Polaris) is the star which appears to be above (at the zenith) of the North geographic pole of the Earth. The altitude of Polaris is the same as the latitude of the observer.
Pollution
Something 'unnatural' and unwanted. A stream may be polluted (has pollution) by nitrogenous waste from cattle and fertilizers. Pollution in the sea may consist of engine oil, or plastic.
Something which damages the environment into which it is introduced.
Pontoon
n A floating structure, a walkway, alongside which boats may be moored, typical of marinas. Unlike a wharf, or quay or pier, a pontoon moves up and down with the tide so remaining a fixed distance above or below the gunwale of a moored boat.
Poor
Poor visibility is less than 2 miles.
Poop deck
Located at the stern, this short deck takes its name from the Latin word puppis - which means after deck or rear. The poop deck is higher, shorter and further aft than the quarter deck.
A vessel is said to be 'pooped' when the sea breaks over its stern.
n A flat-bottomed vessel the deck of which is level with the sheer-strake. The pontoon boat on the right is a catamaran supported on two aluminium floats.
Port
adj The left hand side of the boat, looking forward.
n An opening in the side of the boat: a gunport was an opening for the muzzle of a cannon. A portlight is a window (often circular) which may or may not open.
An entry port is an opening in (usually the left) side of the ship through which passengers and crew pass.
n A harbour where passengers may be embarked and disembarked and cargo may be loaded and unloaded.
The rivers Stour and Orwell meet at a natural harbour between Felixstowe and Harwich. Felixstowe is a deep-water port for container ships. Harwich is a port for passenger vessels, including North Sea ferries and Thames barges.
In port (a harbour) the left hand side of a ship was usually brought alongside the wharf because the steering oar was on the starboard (steer-board) side. Passengers and crew embarked and disembarked through the entry port, which was an opening in the left hand side of the boat. The left hand side became known as the larboard, a contraction of loading board: the board was the top-most plank or wale. In a gale of wind at sea the word ‘larboard’ was easily confused with starboard, and was replaced with ‘port’ during the Napoleonic wars.
n A sweet fortified wine made in Portugal, originally by the British.
Portsmouth Yardstick
A handicap measurement used in yacht racing.
Port tack
A sailing vessel is on the port tack when the wind is on its port side and its main boom is out to starboard.
On a square-rigged ship the lower left corner of the course sails, the tack, would be tacked down to the port bow.
Position
Where the ship is.
Position line
A straight or curved line, often drawn on a chart, somewhere along which the vessel lies.
If a compass bearing is taken from the ship to, say, a lighthouse and that line is drawn on a chart, then the ship can be assumed to lie somewhere along that line.
If the altitude of a star is measured with a sextant a curved line (indeed, a complete circle) can be drawn on a chart; at all points on the circle the star will have the same altitude. The ship lies somewhere on the curved position line.
See fix
Praam
A small boat, probably of Dutch origin, which has no stem and therefore no bows but has a transom at both the forward and after end.
The Mirror dinghy is an ubiquitous example of a sailing praam.
Pram
n A contraction of 'praam', qv.
n A contraction of 'perambulator': a baby carriage.
Precipitation
Precipitation is something which falls from the air, such as rain, sleet, snow, hail (but not frogs). Mist and fog are not, strictly, precipitation.
See Weather.
Preferred channel marker
These buoys are placed at the point where one channel becomes two, when returning to harbour: they show which is the preferred channel according to the local Harbourmaster. They do not prescribe which channel you must take: the chart, or the pilot book, will usually indicate, directly or indirectly, the reason for the preference.
In IALA-A the buoy is a red can with a horizontal green stripe where the preferred channel is to starboard; and a green cone with a horizontal red stripe where the preferred channel is to port. The red can carries a red light Fl.R.(2+1) and the green cone carries a green light FL.G.(2+1).
In IALA-B the buoy with the same purpose is called a Junction buoy. It has a number of red and green horizontal bands; the uppermost band indicates the preferred channel. Where the uppermost band is red, the preferred channel is to port; where the uppermost band is green, the preferred channel is to starboard.
Press gang
A group of sailors, led by a midshipman or petty officer, sent into the town and surrounding countryside to recruit sailors. Men were often recruited by force (pressed) or by trickery. They might be offered a tankard of ale at the bottom of which they would find a shilling*. They were then deemed to have accepted the King's shilling; to have accepted employment in the Navy.
*In the days before decimalisation of the British currency a shilling was one twentieth of a pound. There were 12 (old) pence to a shilling.
Pressure
Atmospheric pressure is the force per unit area exerted on a surface by the weight of air above that surface.
The standard atmosphere (symbol: atm) is a unit of pressure equal to 1013.25 millibars.
(one bar is 1000 millibars, or 14.5 lbs/sq in, or 29.53 inches of mercury)
Atmospheric pressure varies widely on Earth, and these changes are important in generating weather and climate.
On a synoptic chart the isobars are curved lines which link points of equal pressure; the isobars are usually drawn 4 millibars apart. Points at which the air pressure is, eg, 984mb, would be linked by a curved line which would enclose areas of lower pressure; areas of higher pressure would lie outside the area enclosed. Points at which the air pressure is, e.g., 1018mb, would be linked by a curved line which would enclose areas of higher pressure; areas of lower pressure would lie outside the area enclosed.
On this synoptic chart of the North Atlantic there is a deep depression (971 millibars) SE of Greenland around which strong winds (red arrows) rotate anticlockwise. There is high pressure (1028 millibars) over the British Isles, the Bay of Biscay and the North Sea around which the lighter winds rotate clockwise.
The strength of a wind is determined by the pressure gradient; the difference in pressure between the high pressure centre & the low pressure centre and the distance between the two. More closely spaced isobars indicate a steeper pressure gradient (stronger winds); more widely spaced isobars indicate less strong winds
Warmer air is less dense (lighter) than colder air; warmer, rising air is at a lower pressure than the surrounding air masses. Colder air is more dense (heavier) than warmer air; colder, falling air is at a higher pressure than the surrounding air masses.
Because of the Coriolis effect falling air masses rotate clockwise in the Northern hemisphere, anticlockwise in the Southern hemisphere. Rising air masses tend to rotate anticlockwise in the Northern hemisphere, clockwise in the Southern hemisphere.
In the North Atlantic the cyclonic winds around a depression rotate anticlockwise around the region of low pressure.
When moving air meets a flat surface it ’piles up’ against the surface, creating a region of higher pressure. As the moving air spills around the edges of the surface it often becomes turbulent; a region of lower pressure appears on the downwind (leeward) side of the surface. The difference in pressures creates a force which tends to move the surface downwind (to leeward).
When the flat surface is normal (at right angles) to the wind the pressure difference, and the turbulence, will be maximal. When the flat surface is parallel to the wind direction there will be no pressure difference and no turbulence.
An empty cardboard box will be blown downwind; a strong wind will move a person downwind; a very strong wind will displace a building.
If the surface is shaped like a drop of water the wind will tend to ‘stream’ around it; there will be a difference in pressure between upwind and downwind, but there may be little or no turbulence on the downwind side.
A sail is neither a flat surface nor a water drop; it is a thin sheet of material cut and stitched so that it has a curved shape in three dimensions.
With the wind ‘parallel’ to a sail (zero angle of attack) its shape will allow it to billow and flap side to side. Pressure differences will change from moment to moment. The movement will create noise and cause damage to the sail.
With the wind at right angles to the sail (90° angle of attack) it will fill with air which will spill around the edges and become turbulent. The downwind side will have a ‘bubble’ of stationary air at a lower pressure.
With the sail at a low angle of attack moving air will flow along both sides of the sails without turbulence (it will be laminar). The moving air on the downwind side will be at a lower pressure than the air on the upwind side; the pressure difference will create a force which tends to move the sail toward the lower pressure. For each sail there is an angle of attack at which the pressure difference is greatest, and the driving force is greatest.
Most square-rigged and fore-and-aft sails achieve their greatest driving force when the moving air is laminar; when it becomes turbulent (at high angles of attack) the driving force falls significantly.
By contrast, ‘crab claw’ and lateen sails achieve their highest driving forces at high angles of attack with helical turbulence from the leading edges.
Preventer
A line from the boom to a cleat near one of the bows prevents an accidental gybe when sailing by the lee. Once known as a guy.
A preventer backstay is like a running backstay; it prevents the mast from buckling under the load of the forestay.
Prime meridian
An imaginary line across the surface of the earth passing through the North Pole, Greenwich (in East London) and the South Pole.
The Prime, or Greenwich, meridian is at zero degrees West and zero degrees East. It is the meridian from which all time zones are measured and is the datum for astronavigation calculations.
Privateer
A privately owned ship authorized by a state to attack enemy ships.
See Pirate
Prize
n An award for winning a race, or for a specially meritorious act.
n During the Age of Sail an enemy vessel captured at sea. The captain of the winning ship would place a prize crew, under the command of a junior lieutenant or midshipman, to take the prize home to a prize agent who would buy it. The money would be shared among the officers and crew of the winning ship and with the crew of other ships in sight at the time of capture.
Proa
A long slim sailing boat with cross-beams (aka) to a small float (ama) which resists capsize. The ama is usually kept to windward. The boat is symmetrical end to end.
Proas do not change tack to windward: instead they 'shunt' by turning away from the wind and then sailing 'backwards' on the new heading; the erstwhile stem becomes the new stern and vice versa.
Projection
The fundamental problem of cartography is that no map from the sphere to the plane can accurately represent both angles and areas. In general, area-preserving map projections are preferred for statistical applications, while angle-preserving (conformal) map projections are preferred for navigation.
Promontory
A rock, or a high point of land, projecting out into the sea. Its extremity is a cape or a headland.
Protractor
An instrument for measuring angles and for drawing angles.
The central circle of the Portland Plotter is a protractor.
The Douglas protractor, unlike others which are semicircular, is a square.
Propeller
A set of rotating, angled blades mounted on a shaft connected to an engine. As the shaft, and therefore the blades, rotates the water is pushed aft (or ahead) and the boat, by reaction, is pushed ahead (or astern).
Many propellers have fixed blades. The direction of rotation, and the direction of the vessel, is altered by a gearbox on the propeller shaft.
The propellers of some sailing vessels are designed to fold when not rotating, so reducing drag.
The blades of some propellers can be angled at will by a concentric shaft around the drive shaft. The engine speed can be held constant and the speed (or direction) of the vessel changed by altering the pitch of the propeller.
Propeller (prop) walk
As a propeller rotates, in addition to pushing the water aft or forward, it behaves as a paddle wheel and pushes the water sideways. The water at the top of the propeller is slightly less dense than the water at the bottom, so the bottom of the propeller pushes the water sideways more effectively, and pushes the stern to one side. Normally, when steaming ahead, prop walk is counteracted by a small angle of the rudder. At very slow speeds the propwalk may move the stern of the vessel sideways.
Power-driven vessels often reduce speed by reversing their propellers: where the vessel has a single screw the prop-walk of reversing may cause the vessel to yaw significantly.
Conversely, when manoeuvring at slow speeds prop-walk can be used to advantage.
On larger vessels, two (or more) propellers are arranged to rotate in different directions; each one neutralizes the prop-walk of the other.
Outboard motors are available which have two propellers on concentric shafts rotating in different directions; the prop-walk of each propeller negates that of the other.
Provision(s)
n The food and drink to be taken on board and served to the crew.
v The act of taking provisions on on board; to provide food and drink for the crew.
Prow
A poetic alternative to stem. A prow is often higher and more ornate than a stemhead.
Originally, the name given by seamen to the beak, or pointed cutwater, of a galley, polacre or xebec.
Pulley
A pair of plates (known as cheeks) between which is a grooved wheel (known as a sheave) around which a rope passes. On board ship a pulley is known as a block.
Pulleys are used to change the direction in which a rope pulls or to increase the power of pulling a rope.
See Purchase.
Pulling boat
A boat which is moved (given way) by pulling on the oars.
In the 21st century, a rowing boat (or, in the USA, a row-boat).
Pulpit
The rail around the stem and bows of the boat, so-called because of its similarity to the pulpit in a Christian church.
Pump
A device for moving fluids from place to place.
A bilge pump moves water (and small debris) from the bilges of a boat to the sea.
A fuel pump moves fuel (petrol or diesel) from the fuel tank to the engine. On a diesel engine the injector pump moves diesel fuel from the low-pressure lift pump to the injectors at very high pressure.
Water pumps move fresh water from a storage tank to the galley. A separate raw water pump may move sea water to the galley.
At the engine, a water pump moves cooling water around the internal galleries of the engine block. Cooling water might be raw water from the sea or river, or it might be fresh water recirculating through a radiator.
At the heads, a handpump moves sewage from the pan to either the sea or a holding tank. By moving a lever, the same pump moves sea water through the pan to clean it.
An air pump (blower) removes fumes from the engine room before the engine starts.
An air pump (Turbocharger) increases the amount of air into the cylinder of an internal combustion engine.
An air pump (compressor) is used for filling the air tanks of divers.
An air pump (fan) is used for recirculating air within the accommodation so that it seems cooler.
A refrigerant pump (compressor) compresses the refrigerant in a refrigerator or freezer so that the heat can be taken from it.
Pumps may be powered by hand, by electricity, by their own internal combustion engine or directly by the boat's engine.
Punt
A long, flat-bottomed boat, moved by the boatman standing on a platform at the stern and pushing a pole against the bottom of the river.
Originally used alongside a vessel to stand on whilst working at the topsides.
Punts were widely used in the East of England for hunting wildfowl and for fishing. The Mersea duckpunt has become a minimalist recreational sailing vessel.
Purchase
An arrangement of a line and one or more blocks, either to increase pulling power or to change the direction of pulling a load.
A whip consists of a block with a single sheave; the block may be attached to a yard. A single line rove through the block allows weights to be lifted from the deck and lowered down through hatchways. There is no mechanical advantage; the force exerted on the fall of the line is the same as the weight to be lifted (neglecting friction).
The gun tackle (above) offers a mechanical advantage of 2; a weight of two units on the lower block can be lifted by a weight (force) of one unit on the fall.
The luff (watch or tack) tackle offers a mechanical advantage of 3 for lifting weights with the hook; if the hook is fixed to the deck and the upper block is attached to the luff of a sail, or the boom of a balanced lug, it offers a mechanical advantage of 4.
The mechanical advantage is equal to the number of lines rove through the block which moves, neglecting friction. Friction in the purchase increases with the number of blocks and the weight of the item to be moved.
Each of the tackles illustrated above is "rove to disadvantage" (the upper block, from which the fall emerges, changes the direction of effort but adds no mechanical advantage. When "rove to advantage" the fall is pulled from the block which moves.
The "Three Fold Purchase" has three sheaves in each block. the mechanical advantage on the lower block is six-fold (six lines support the lower block).
Purser
The person aboard ship responsible for financial transactions such as provisions, victuals, clothing, stores.
In the British Royal Navy, pronounced 'pusser'.
Pushpit
The slang name for the taffrail.
The protective rail around the stem and bows of a boat has been called a 'pulpit' from its similarity to the pulpit of a Christian church. By a twist of meaning the similar structure at the stern has been called a 'pushpit'.
Pyrotechnic
An adjective describing devices which operate with fire or explosives. These devices include flares, rockets, incendiary shells.